In this study, different parameters of uterine artery Doppler ultrasound predicted preeclampsia differently. In particular, the sensitivity and specificity were low when the parameters PI and RI were used alone, whereas they were high when S/D was used. Uterine artery Doppler ultrasound is an important method for evaluating high-risk pregnancies with preeclampsia during early pregnancy. Many studies have explored the utility of Doppler indicators in predicting preeclampsia, but the results are controversial. Uterine arterial blood flow and RI are commonly used predictors of preeclampsia. A meta-analysis indicated that uterine artery RI and PI predicted preeclampsia more accurately than blood flow [20]. However, other studies have shown that an RI of ≥ 0.58 and a blood flow rate of > 105 mL/min were more accurate predictors at approximately 20 weeks of gestation [21, 22], but these findings might vary depending on the research object and technique used.
The superiority of the Doppler index of the right uterine artery over that of the left in predicting preeclampsia is controversial. One study showed that an RI of ≥ 0.61 and a blood flow rate of > 123 mL/min for the right uterine artery were independent predictors of preeclampsia [23]. However, another study demonstrated that the predictive abilities of left and right uterine artery indices are equivalent [24], which may be attributable to differences in individual arterial structure and blood flow. The position of the placenta also affects Doppler prediction ability. Investigators have reported that hemodynamic changes in the posterior placenta were more pronounced than those of other placental locations and that the predictive power of the PI and RI was higher [22]. Other studies have shown that placental position does not affect the predictive value of the Doppler index [25].
Uterine artery Doppler ultrasound can be used for predicting preeclampsia during pregnancy; however, its predictive ability is constrained by various factors, resulting in differences variable outcomes. To improve prediction accuracy, both sensitivity and specificity need to be considered, but only one predictive indicator, specificity, is most often selected. Excessively high false-positive results lead to excessive intervention, increase maternal anxiety, and even affect the quality of life of pregnant women. Reducing the cutoff value of the Doppler index can improve sensitivity but not specificity, leading to more false-positive results. One meta-analysis showed that a RI of ≥ 0.58 has only 67% specificity, whereas the specificity of a RI of ≥ 0.65 can reach 89% [26]. Other studies have confirmed that the sensitivity of a RI of ≥ 0.58 is as high as 97%, but the specificity is only 63%. When the RI was ≥ 0.65, the sensitivity decreased to 82%, but the specificity increased to 81% [24]. This indicates that under the same conditions, higher RI cutoff values can achieve higher specificity.
Many investigators use receiver operating characteristic curve analysis and choose Doppler parameters with higher specificity as predictive indicators. Studies have shown that when specificity reaches 85%, RI ≥ 0.63 and PI ≥ 1.45, and an RI of ≥ 0.66 in the posterior placenta is a predictor of preeclampsia [23]. Another study demonstrated that 90% specificity is achieved by an RI of ≥ 0.715 and a PI of ≥ 2.145 in the UtAs [27]. This further confirms that a higher Doppler index cutoff value can help achieve higher specificity. Other investigators have used different methods to improve the specificity of Doppler examination. For example, using a bilateral uterine arterial RI of ≥ 0.63 and PI of ≥ 1.45, Velauthar et al. achieved 89% specificity [28]. Alternatively, to establish a predictive model with high specificity, logistic regression analysis can be performed with a combination of risk factors and Doppler indicators to identify variables with high specificity.
Of the 40 included studies, 9 had populations from India and 9 from Thailand; thus, the findings may not be globally representative. Also, the meta4diag program package in R software, which was used for the analysis, did not include a heterogeneity test. Therefore, additional studies with more convincing results may be needed to verify the utility of Doppler parameters in predicting preeclampsia.